Joined Object to Mesh Separates when Moved
Maybe, in the Properties panel &gt; Object Data &gt; Vertex Groups, remove the rose from all groups (down arrow dropdown menu &gt; Remove from All Groups) then assign it to the vertex group you want.
Another way to fix this is to remove the rose vertices from all vertex groups, to separate it as a second object, then, in Object mode, select the rose, shift select the shirt, switch to Edit mode, select one or 3 vertices of the shirt and press CtrlP &gt; Make Vertex Parent, it will make the rose follow these vertices.